Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$28.50	13.418%	$32.3241	$32.32	$32.30	$32.30
Purchase #2	$212.41	13.679%	$241.4656	$241.47	$241.45	$241.50
Purchase #3	$99.25	5.292%	$104.5023	$104.50	$104.50	$104.50
Purchase #4	$16.43	12.231%	$18.4396	$18.44	$18.45	$18.40
Purchase #5	$79.68	4.433%	$83.2122	$83.21	$83.20	$83.20
Purchase #6	$47.55	12.415%	$53.4533	$53.45	$53.45	$53.50
Purchase #7	$203.94	8.434%	$221.1403	$221.14	$221.15	$221.10
7 purchase totals =	$687.76		$754.5374	$754.53	$754.50	$754.50